Historically, systems for photographing the ground or the like from satellites or aircrafts have been used. In such systems, a single image object is often photographed by performing simultaneous capturing of a panchromatic image with high resolution and a multispectral image with a resolution lower than that of the panchromatic image. A panchromatic sensor is configured to capture an image in all wavelengths of visible and near-infrared light, and a multispectral sensor is configured to capture an image only in particular wavelengths such as blue light or red light. The multispectral sensor is capable of capturing an image of a particular color. However, the amount of light per unit area received by the multispectral sensor is smaller as compared with the panchromatic sensor. As the amount of light per pixel received by the sensor decreases, noise components increase relative to the signal components. This makes it difficult to capture images of good quality. In order to avoid such things, in the multispectral sensor, the amount of received light is increased by lowering the resolution and enlarging the image area per pixel as compared with that of the panchromatic sensor. In such a system simultaneously capturing both a low resolution multispectral image and a high resolution panchromatic image, pan-sharpen processing is performed to create a high resolution color image by combining these two images In the pan-sharpening processing, a high resolution color image is created, for example, by decomposing components of each pixel of a multispectral image into a brightness component, a hue component and a chroma component, and replacing the brightness component with a component of a panchromatic image with high resolution. Incidentally, to reduce noise included in an image is a general issue and not limited to a high resolution color image created by the pan-sharpen processing. Such noise reduction is performed by image processing. Patent Literature 1 describes a method related to noise reduction by image processing.
The method described in Patent Literature 1 is as follows.
The image processing method for reducing noise included in an image includes an image input procedure of inputting an original image comprising a plurality of pixels. The method further includes a multiresolution image creation procedure of decomposing the inputted original image and creating a plurality of low frequency images having sequentially lower resolutions and a plurality of high frequency images having sequentially lower resolutions, and a noise reduction processing procedure of performing noise reduction processing on each one of the low frequency images and the high frequency images. The method further includes an image acquiring procedure of acquiring an image in which noise is removed from the original image on the basis of results of the low frequency images with noise reduced and the high frequency images with noise reduced.